The need for flame resistant polymeric compositions resulted in the development of a field of special technology and a relevant body of knowledge. Among the successful developments, particular mention might be made of alkali metal salts which incorporation in polycarbonates was reported in U.S. Pat. Nos. 3,775,367 and 3,836,490 and in British Pat. No. 1,370,744. Improved flammability of polycarbonate resins upon the addition of organic chlorine compounds have been disclosed in U.S. Pat. No. 3,357,942, in DOS Nos. 2,122,300, 2,153,101 and 2,243,226. German published specification DOS No. 2,013,496 is noted to mention tetrachlorophthalic anhydride as a suitable flame retarding agent in polycarbonates.
Further of interest in this connection is U.S. Pat. No. 4,208,489 which discloses certain tetrahalogenophthalimides as flame retarding agents in polycarbonate compositions, and U.S. Pat. No. 3,873,567 and British Patent Specification No. 1,287,934, both disclosing imido compounds suitable as flame retarding additives in polymeric compositions. It is noted that U.S. Pat. No. 3,873,567 discloses a wide variety of bromine substituted imides suitable as flame retarding agents in polymeric resins including polycarbonates yet, the disclosed compounds have generally a high melting temperature which renders them insoluble in polycarbonate resins at the processing temperatures of this resin.